Extended Reach Rotary Drilling Devices
In rotary drilling operations, a drill bit is attached to the end of a bottom hole assembly which is attached to a drill string comprising drill pipe and tool joints which may be rotated at the surface by a rotary table or top drive unit. The weight of the drill string and bottom hole assembly causes the rotating bit to bore a hole in the earth. As the operation progresses, new sections of drill pipe are added to the drill string to increase its overall length. Periodically during the drilling operation, the open borehole is cased to stabilize the walls, and the drilling operation is resumed. As a result, the drill string usually operates both in the open borehole and within the casing which has been installed in the borehole. Alternatively, coiled tubing may replace drill string in the drilling assembly. The combination of a drill string and bottom hole assembly or coiled tubing and bottom hole assembly is referred to herein as a drill stem assembly. Rotation of the drill string provides power through the drill string and bottom hole assembly to the bit. In coiled tubing drilling, power is delivered to the bit by the drilling fluid pumps. The amount of power which can be transmitted by rotation is limited to the maximum torque a drill string or coiled tubing can sustain.
During the drilling of a borehole through underground formations, the drill stem assembly undergoes considerable sliding contact with both the steel casing and rock formations. This sliding contact results primarily from the rotational and axial movements of the drill stem assembly in the borehole. Friction between the moving surface of the drill stem assembly and the stationary surfaces of the casing and formation creates considerable drag on the drill stem and results in excessive torque and drag during drilling operations. The problem caused by friction is inherent in any drilling operation, but it is especially troublesome in directionally drilled wells or extended reach drilling (ERD) wells. Directional drilling or ERD is the intentional deviation of a wellbore from the vertical. In some cases the angle from the vertical may be as great as ninety degrees from the vertical. Such wells are commonly referred to as horizontal wells and may be drilled to a considerable depth and considerable distance from the drilling platform.
In all drilling operations, the drill stem assembly has a tendency to rest against the side of the borehole or the well casing, but this tendency is much greater in directionally drilled wells because of the effect of gravity. As the drill string increases in length or degree of vertical deflection, the amount of friction created by the rotating drill stem assembly also increases. To overcome this increase in friction, additional power is required to rotate the drill stem assembly. In some cases, the friction between the drill stem assembly and the casing wall or borehole exceeds the maximum torque that can be tolerated by the drill stem assembly and/or maximum torque capacity of the drill rig and drilling operations must cease. Consequently, the depth to which wells can be drilled using available directional drilling equipment and techniques is limited.
Reduction of friction is a key requirement in such ultra-extended reach subterraneous oil and gas rotary drilling applications. One method for reducing the friction caused by the contact between the drill stem assembly and casing (in case of a cased hole) or borehole (in case of an open hole) is improving the lubricity of drilling muds. In industry drilling operations, attempts have been made to reduce friction through, mainly, using water and/or oil based mud solutions containing various types of expensive and often environmentally unfriendly additives. Diesel and other mineral oils are also often used as lubricants, but there is a problem with the disposal of the mud. Certain minerals such as bentonite are known to help reduce friction between the drill stem assembly and an open borehole. Materials such as Teflon have been used to reduce friction, however these lack durability and strength. Other additives to include vegetable oils, asphalt, graphite, detergents and walnut hulls, but each has its own limitations. While these muds have had some benefit, the disposal of mud is an issue. Additionally, a bigger issue is the fact that the COF increases with increasing temperature, especially with water-based muds.
Yet another method for reducing the friction between the drill stem assembly and the well casing or borehole is to use a hard facing material on the drill string assembly (also referred to herein as hardbanding or hardfacing). U.S. Pat. No. 4,665,996, herein incorporated by reference in its entirety, discloses the use of hardfacing the principal bearing surface of a drill pipe with an alloy having the composition of: 50-65% cobalt, 25-35% molybdenum, 1-18% chromium, 2-10% silicon and less than 0.1% carbon for reducing the friction between the drill string and the casing or rock. As a result, the torque needed for the rotary drilling operation, especially directional drilling, is decreased. The disclosed alloy also provides excellent wear resistance on the drill string while reducing the wear on the well casing. Hardbanding may be applied to portions of the drill stem assembly using weld overlay or thermal spray methods.
While the hardbanding has been effective in protecting tool joints to some extent, the carbide particles are known to cause severe abrasive wear of the casing material, thus limiting the effectiveness of this technique.
Another method for reducing the friction between the drill stem assembly and the well casing or borehole is to use aluminum drill string because aluminum is lighter than steel. However, the aluminum drill string is expensive and is difficult to use in drilling operations, and it is not compatible with many types of drilling fluids (e.g. drilling fluids with high pH).
U.S. Pat. Nos. 7,182,160, 6,349,779 and 6,056,073 disclose the designs of grooved segments in drill strings for the purpose of improving fluid flow in the annulus and reducing contact and friction with the borehole wall.
Still another problem encountered during subterraneous rotary drilling operations, especially directional drilling, is the wear on the casing and drill stem assembly that occurs when the metal surfaces contact each other. This abrasion between metal surfaces during the drilling of oil and gas wells results in excessive wear on both the drill stem assembly and the well casing. Presently, one preferred solution to reduce wear of drill stem assemblies is to hardface portions of the drill stem assembly. A tungsten carbide containing alloy, such as Stellite 6 and Stellite 12 (trademark of Cabot Corporation), has excellent wear resistance as a hardfacing material. Hardfacing protects the drill stem assembly, but it tends to cause excessive abrading of the well casing. This problem is especially severe during directional drilling because the drill stem assembly, which has a tendency to rest on the well casing, continually abrades the well casing as the drill string rotates. In addition, some of these hardfacing alloys, such as tungsten carbide, may make the friction problem worse.
Coated Sleeve Oil and Gas Well Production Devices:
In addition to the subterraneous rotary oil and gas drilling devices, friction is also an issue in oil and gas well production devices. Oil and gas well production suffers from basic mechanical problems that may be costly, or even prohibitive, to correct, repair, or mitigate. Friction is ubiquitous in the oilfield, devices that are in moving contact wear and lose their original dimensions, and devices are degraded by erosion, corrosion, and deposits. These are impediments to successful operations that may be mitigated by selective use of coated sleeved oil and gas well production devices as described below. These oil and gas well production devices include, but are not limited to, drilling rig equipment; marine riser systems; tubular goods; wellhead, trees, and valves; production equipment including artificial lift equipment, completion strings and equipment; formation and sandface completions; and well intervention equipment.
Petrochemical and Chemical Industry Equipment and Devices:
Components for equipment in petrochemical and chemical production suffer from degradation ranging from mechanical and chemical effects. For instance, components undergo wear due to repeated rubbing of surfaces resulting in failure requiring repair or replacement. Under certain circumstances, the debris produced by wear may also contaminate the product making it unacceptable. In addition to wear, excessive friction between surfaces could also enhance the energy required for the operation. Higher energy costs may also be realized while pumping fluids in the operation due to excessive friction or resistance between the fluid and the surface of the component that transmits it. Another example of degradation of components may relate to corrosion where the components need to be replaced periodically. Corrosion may also lead to fouling in the inner diameter of heat exchanger tubulars resulting in degradation of the heat transfer efficiency. These are all potential impediments to successful petrochemical operations that may be costly, or even prohibitive, to correct, repair, or mitigate.
Non-limiting exemplary applications of such coatings include extruders, barrels, gear boxes, bearings, compressors, pumps, pipes, tubing, molding dies, valves, and reactor vessels.
Need for the Current Disclosure:
Given the expansive nature of these broad requirements for extended reach rotary drilling devices, coated sleeve oil and gas well production devices and petrochemical and chemical industry equipment and devices, there is a need for low friction coatings with improved properties, such as friction, wear, abrasion, corrosion, erosion, and deposits. Given the operating environments for these applications, which typically include high loads and severe abrasive conditions, traditional and conventional low friction coatings (e.g., graphite, MoS2, WS2) may not meet durability requirements in some cases. Thus, there is a to need to develop low friction coatings that demonstrate adequate durability in these environments, through improved abrasion resistance and reduced wear on both the coated part as well as the counterface material (e.g. casing steel), relative to prior art coatings.